New York City Mayor and businessman Michael Bloomberg has hit the $1bn (£630m) mark in donations to his alma mater, Johns Hopkins University.

Mr Bloomberg became what is believed to be the first person to give so much money to a single US university with his most recent $350m (£221m) earmark to help expand the school's research on cross-discipline issues including global health and urban revitalization.

Most of this latest gift - $250m - will be part of a larger effort to raise $1bn to foster cross-disciplinary work on global issues.

The money will initially will be used toward hiring faculty for work on issues such as individualised health care delivery, water resource sustainability and the science of learning.

The remaining $100m will go toward need-based financial aid for undergraduate students in the form of 2,600 Bloomberg scholarships.

The Baltimore university said this gift brings Mr Bloomberg's giving to the institution to just over $1.11 billion in the 49 years since he graduated - including his first gift of $5 in 1965, a year after he took his bachelor's degree in engineering.

"Johns Hopkins University has been an important part of my life since I first set foot on campus more than five decades ago," Mr Bloomberg said in a statement released by the university.

He added: "Each dollar I have given has been well-spent improving the institution and, just as importantly, making its education available to students who might otherwise not be able to afford it."

The New York mayor has remained closely involved with the university, including serving on its board of trustees from 1996 to 2002.

Mr Bloomberg's other gifts have included $120m (£76m) toward building the children's section at Johns Hopkins Hospital in honour of his late mother.